Simple model for coupled magnetic and quadrupolar instabilities in uranium heavy-fermion materials.
Simple model for coupled magnetic and quadrupolar instabilities in uranium heavy-fermion materials.
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铀重费米子材料中耦合磁和四极不稳定性的简单模型。
DOI：
10.1103/physrevb.48.3783
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发表时间：
1992
期刊：
影响因子：
--
通讯作者：
Cox
中科院分区：
文献类型：
--
作者：
Líbero;Cox
我们给出了六方铀重费米子化合物中一个简单的定域力矩模型相图的平均场计算。该模型考虑了非Kramers四极双重态基态与单重态激发态的磁性耦合，有利于面内van Vleck磁性，正如对UPT[sub3]所猜测的那样。定义该模型的哈密顿量在磁矩和四极矩中都是类似海森堡的。计算中没有包括近藤效应物理。我们的主要结果是：(I)对于零位间四极耦合，磁有序是通过高于临界位间磁耦合强度的一级跃迁实现的，当耦合强度较高时变为二阶；(Ii)对于有限的位间四极耦合，在低于二阶四极有序转变的温度下，最小磁耦合值增加，但(A)磁有序温度高于该值，以及(B)相图中一、二阶转变的有序性颠倒。通过考虑Ginsburg-Landau自由能的一般结构，我们认为近藤效应不会改变相图的形状，但会改变相变发生的量化值。
We present a mean-field calculation of the phase diagram of a simple model of localized moments, in the hexagonal uranium heavy-fermion compounds. The model considers a non-Kramers quadrupolar doublet ground state magnetically coupled with a singlet excited state, favoring in-plane van Vleck magnetism, as has been conjectured for UPt[sub 3]. The Hamiltonian that defines the model is Heisenberg-like in both magnetic and quadrupolar moments. No Kondo-effect physics is included in the calculations. Among our main results are (i) for zero intersite quadrupolar coupling, the magnetic order is achieved by a first-order transition above a critical intersite magnetic coupling value, which becomes second order at higher coupling strengths (ii) for finite intersite quadrupolar coupling, at temperatures below a second-order quadrupolar ordering transition, the minimal magnetic coupling value is increased, but (a) the magnetic ordering temperature is enhanced above this value, and (b) the ordering of first- and second-order transitions in the phase diagram is reversed. By considering the general structure of the Ginsburg-Landau free energy, we argue that the Kondo effect will not modify the shape of the phase diagram, but will modify the quantitative values at which transitions occur.